This invention relates generally to systems for controlling an internal combustion engine, and more specifically, to a system for optimizing engine cylinder combustion in a direct injection two stroke engine.
Many known internal combustion engines include an electronic control unit (ECU) for controlling at least some operations of the engine. In a typical implementation, an ECU is electrically connected to engine components such as the engine ignition, lubrication pumps, water circulation system (if any) and fuel injectors. The ECU controls operational parameters, such as timing of the engine ignition and fuel injection, in accordance with a pre-programmed control program according to predetermined values or setpoints stored in system memory and dependant upon an operational state of the engine. The ECU looks up one or more of the stored parameter values corresponding to a state determined by various transducers or sensors, and other parameters are calculated, corrected, or adjusted based upon the engine parameter values stored in system memory so that the engine is operated at optimal levels, or nearly optimal levels, at all stages of operation.
In at least some engine applications, however, such as in marine engine outboard motors, these control schemes can be problematic because a given motor may be used in conjunction with various boat platforms that uniquely impact motor operation. In some applications, such as pontoon boats, actual engine operation is less than optimal in certain operating ranges, particularly at high RPM (e.g. 3500 to 4500 RPM) and low loads (e.g., about 15% of wide open throttle), while in other operating ranges, optimal engine operation is achieved without modification of the predetermined system values.
In an exemplary embodiment of the invention, a control unit is provided for an internal combustion to avoid problematic operating conditions in certain applications, such as when the engine is used with a pontoon boat. The engine includes an engine block comprising a plurality of cylinders, and each of the cylinders is operable in a homogenous combustion mode and a stratified combustion mode in response to an engine throttle position. The control unit is programmed to control each of the cylinders to operate in the stratified combustion mode at throttle positions of up to about 20% of wide open throttle; and to switch one of the cylinders to the homogenous combustion mode at a throttle position of about 20% of wide open throttle. As such, the combustion mode is switched from the stratified combustion mode to the homogenous combustion mode at a higher throttle opening that more capably supports increased fuel injection quantities of homogenous combustion in the engine cylinders. Problematic conditions of conventional systems due to switching of engine cylinders to homogenous combustion at restricted throttle openings is therefore avoided, a problem which is magnified at higher RPMs encountered near the cylinder switch points in pontoon boat applications.
More specifically, in a four cylinder embodiment, each of the engine cylinders are switched from the stratified combustion mode to the homogenous combustion mode at throttle positions of about 20% to about 42%, and then operated in the homogenous combustion mode at throttle positions greater than about 42% of wide open throttle. Thus, less than optimal engine operating ranges in pontoon boat applications are avoided, and improved performance in pontoon boat applications is achieved.